ROADS AND BRIDGES 3OI 



ditions. It is not always necessary to make a plan for 

 the bridge, as the representative of each of the compet- 

 ing bridge-building firms may be willing to submit a 

 plan for such a structure as his establishment is qualified 

 to erect and deems best for the purpose. Such plans can 

 be referred to some authority on bridge structures as 

 well as to the resident engineer. Competing firms will 

 use care to have their plans well made if they are re- 

 quired to submit their plans to well-known experts. 



In the construction of culverts and small bridge struc- 

 tures permanency is a very important element. The 

 wooden culverts of the pioneer community should be 

 replaced as rapidly as possible with iron pipes, sewer 

 pipes, stone archways, cement structures, concrete rein- 

 forced with iron, or with small bridges of a combina- 

 tion of iron, cement, stone and wood. All these forms 

 of bridges are comparatively expensive and cannot be 

 afforded in the early days 

 of the community. It is 

 not wise to undertake to 

 reconstruct all the 

 bridges of a district at once, 

 but by making a few per- 

 manent structures each 



year the county or town- Figure 176 stone culvert 



ship will eventually have 



the waterways beneath its roads made of such enduring 

 materials that their reconstruction every few years, neces- 

 sary where wood was used, will be a thing of the past. 



Concrete culverts. The following statement by Hon. 

 Thomas McDonald, of the Iowa highway commission, 

 gives some explicit directions for making culverts. As 

 a rule, it is wise to purchase forms of reinforcing bars 

 manufactured especially for that purpose. 



" Unless the cost of concrete materials is very cheap, 

 and unless the haul is short, the flat top form of con- 



